Disease relevance of RANBP1

• Mutations in the nuclear export signal of human ran-binding protein RanBP1 block the Rev-mediated posttranscriptional regulation of human immunodeficiency virus type 1 [1].
• RanBP1, a velocardiofacial/DiGeorge syndrome candidate gene, is expressed at sites of mesenchymal/epithelial induction [2].

High impact information on RANBP1

• We now show that Npap60 (also called Nup50), a protein previously believed to be a structural component of the NPC, is a Ran binding protein and a cofactor for importin-alpha:beta-mediated import [3].
• The Ran-binding protein RanBP2 contains four of these domains and constitutes a large part of the cytoplasmic fibrils that extend from the nuclear-pore complex [4].
• RanBP1 as well as Ran-binding domains of the cytoplasmic nucleoporin RanBP2 promote the release of CRM1 from the NPC [5].
• A role for RanBP1 in the release of CRM1 from the nuclear pore complex in a terminal step of nuclear export [5].
• By biochemical fractionation and reconstitution, we showed that RanBP1 restores nuclear export after the RanQ69L preincubation [5].

Biological context of RANBP1

• RanBP1 is the first member of a new class of proteins regulating the binding and hydrolysis of GTP by Ras-related proteins [6].
• Co-activation of RanGTPase and inhibition of GTP dissociation by Ran-GTP binding protein RanBP1 [6].
• Since the structure of the Ran-RanBP1-RanGAP complex showed RanBP1 to be located away from the active site, we reinvestigated the reaction using fluorescence spectroscopy under pre-steady-state conditions [7].
• These results are consistent with the hypothesis that Ran functions directly in at least two pathways, one, dependent on RanBP1, that affects cell cycle progression and RNA export, and another, independent of RanBP1, that affects nuclear protein import [8].
• Mammalian RanBP1 regulates centrosome cohesion during mitosis [9].

Anatomical context of RANBP1

• In addition, we have identified a fraction of RanBP1 at the centrosome [9].
• Specifically, RanBP1 excess induces splitting of mother and daughter centrioles at spindle poles; the resulting split centrioles can individually organize functional microtubule arrays, giving rise to functional spindle poles [9].
• In addition, RanBP1 is expressed in the forebrain as well as in hindbrain regions previously associated with crest-derived mesenchymal cells [2].
• RanBP1, a velocardiofacial syndrome/DiGeorge syndrome candidate gene, is expressed in the frontonasal processes, branchial arches, aortic arches, and limb buds [2].
• Two Ran-binding proteins, RanBP1 and RanBP2, form discrete complexes with p97 as demonstrated by immunoadsorption from HeLa cell extracts fractionated by gel filtration chromatography [10].

Associations of RANBP1 with chemical compounds

• We found that a novel Ran mutant with four of its five acidic C-terminal amino acids modified to alanine (RanC4A) has an approximately 20-fold reduced affinity for RanBP1 [11].
• A leucine-rich nuclear export signal (NES) near the C terminus of RanBP1 is essential to maintain this distribution [12].
• We now show that RanBP1 accumulates in nuclei of cells treated with the export inhibitor, leptomycin B, and collapse of the nucleocytoplasmic Ran:GTP gradient leads to equilibration of RanBP1 across the nuclear envelope [12].
• A conserved cysteine residue in p97, Cys-158, is required for binding Ran-GDP/RanBP1, but not for binding of Ran-GTP to p97 [13].
• The loss of affinity of RanBP1 for the triphosphate form of RanDeltaC was a result of both a decrease of the association rate and a moderately increased dissociation of the RanDeltaC.RanBP1 complex [14].

Physical interactions of RANBP1

• An in vitro binding experiment showed that RanBP1 binds to RCC1 with the aid of Ran [15].
• The C terminus of fragile X mental retardation protein interacts with the multi-domain Ran-binding protein in the microtubule-organising centre [16].
• RanBP5 binds to RanBP1 as part of a trimeric RanBP1-Ran-RanBP5 complex [17].

Regulatory relationships of RANBP1

• These findings indicate that RanBP1 negatively regulates RCC1 [15].

Other interactions of RANBP1

• Taken together, our results indicate that RanGTP is important for the targeting of export complexes to the cytoplasmic side of the NPC and that RanBP1 and probably RanBP2 are involved in the dissociation of nuclear export complexes from the NPC in a terminal step of transport [5].
• Receptor-mediated nucleocytoplasmic transport is dependent on the GTPase Ran and Ran-binding protein 1 (RanBP1) [11].
• XMog1 and RanBP1 also promote selective GTP loading onto Ran catalysed by the nuclear guanine nucleotide exchange factor, RCC1 [18].
• RBH complex resisted dissociation by RanBP1 and GTP hydrolysis by Ran GTPase activating protein 1 [19].
• A recently found novel Ran-binding protein, RanBPM, however, is localized in the centrosome [20].

Analytical, diagnostic and therapeutic context of RANBP1

• Using site-directed mutagenesis and deletion analysis, we have identified two distinct but overlapping binding domains for Ran-GTP and Ran-GDP/RanBP1 on p97 [13].
• To identify new members of the importin beta family, we used affinity chromatography on immobilized RanGTP and isolated Ran-binding protein (RanBP) 16 from HeLa cell extracts [21].
• Circular dichroism spectra indicate significant changes in the secondary structure of either Ran.GppNHp, RanBP1, or both proteins upon forming a stable complex with each other [14].
• Full-length cDNAs were isolated from a human testis cDNA library and sequence analysis predicted a putative Ran binding protein, a novel member of the importin-beta superfamily of nuclear transport receptors, called RanBP17 [22].
• Here, we characterize the kinetics and equilibrium of the interaction between Ran and RanBP1 by two independent biophysical approaches: fluorescence spectroscopy using analogues of guanine nucleotides and surface plasmon resonance in the BIAcore system [14].

References